Flip chip technology plays an important role in the packaging of semiconductor devices. A flip chip microelectronic assembly includes a direct electrical connection of face down electronic components onto substrates, such as circuit boards, using solder bumps as the interconnects. The use of flip chip packaging has dramatically grown as a result of the flip chips advantages in size, performance and flexibility over other packaging methods.
Recently, copper interconnect post technology has been developed. Instead of using solder bumps, electronic components are connected to substrates by means of copper posts. The copper interconnect post technology achieves finer pitch with minimum probability of bump birdging, reduces the capacitance load of the circuits and allows the electronic components to perform at higher frequencies.
However, copper has a tendency to be oxidized during the manufacturing process. Oxidized copper posts may lead to poor adhesion of an electronic component to a substrate. The poor adhesion may cause serious reliability concerns due to high leakage currents. Oxidized copper posts may also lead to underfill cracking along the interface of the underfill and the copper posts. The cracks may propagate to the underlying low-K dielectric layers or to the solder used to bond the copper posts to the substrate.
Accordingly, there is a need for an improved method to form electrical connections to a semiconductor wafer with robust electrical performance.